The present invention generally relates to power boosters for vehicle brake systems and, more particularly, to an input push rod for applying an input force from a brake pedal to the power booster.
Brake power boosters generally utilize fluid pressure, or differentials thereof, to provide a power assist in applying force to the master cylinder of the brake system. Upon application of an input force on the brake pedal, an input member such as a push rod activates the power booster. The power booster intensifies the force applied to the input push rod by a calibrated amount and transfers the force to a power piston which then moves the master cylinder to apply the brakes at each wheel.
In the past, brake power boosters have incorporated electromechanical switches as part of the booster structure to cause illumination of the vehicle brake lights upon movement of the input rod. For example, power boosters have been designed that include an electrical circuit coupled to the brake illumination control system that causes illumination of the brake lights when the normally-open circuit is closed by a switch. The switch is typically biased in an open position and, in response to travel of the input push rod upon an input force being applied to the brake pedal, moves to a closed position to complete an electrical circuit that illuminates the brake lights.
Brake light control systems that use electromechanical switches to cause illumination of the vehicle brake lights have several drawbacks. For example, the brake booster and input push rod must be designed with additional structures for housing the switch arrangement and for attaching the switch actuation components to the input push rod. These additional structures increase the required space of the power booster which can give rise to installation difficulties when space is limited. Additionally, the electro-mechanical switch must be factory calibrated or adjusted to ensure that the brake lights are not illuminated when the input push rod is in a rest position, but are properly illuminated in response to a predetermined limited travel of the input push rod upon a force being applied to the brake pedal. Further, electro-mechanical switches used in brake light control systems may cause false illumination of the brake lights when the switch is jostled or the driver unintentionally causes travel of the input push rod in a non-braking situation.
For these general reasons, it would be desirable to provide a brake power booster system that accurately and reliably illuminates brake lights of a vehicle in response to a driver""s input on a brake pedal during a braking situation.
The present invention overcomes the foregoing and other shortcomings and drawbacks of brake systems heretofore known and, more particularly, of brake light control systems for causing illumination of brake lights. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
In accordance with the principles of the present invention, an input push rod is adapted to be operatively coupled at one end to a brake pedal and at an opposite end to a power booster of a brake system. The input push rod is capable of applying a force to the power booster that is intensified and applied to a master cylinder of the brake system through a power piston and force output rod to apply the brakes at each wheel. The input push rod includes a sensor that is capable of generating an electrical output having a magnitude that varies with the amount of force applied to the input push rod by the brake pedal. Preferably, the sensor generates an output voltage signal having a magnitude that is generally proportional to the input force applied to the input push rod by the brake pedal. The output voltage signal generated by the sensor is preferably applied to a brake light control system that uses the signal to determine whether the vehicle brake lights should be illuminated. The output voltage signal is also preferably applied to an anti-lock braking control system (ABS) and vehicle stability control system that use this force-related data for controlling other important vehicle functions as well.
In accordance with one aspect of the present invention, the input push rod includes a pair of elongated input push rod members and a coupling member operatively connecting the pair of input push rod members so that the input push rod members extend generally along a common axis. The coupling member comprises a front body portion operatively connected to one of the input push rod members and a rear body portion operatively connected to the other input push rod member. The front and rear body portions of the coupling member are biased relative to each other by a stacked formation of biasing elements, such as by a stack of Belleville washers, so that the pair of elongated input push rod members are effectively biased relative to each other. The pre-load of the washers is adjustable so that the travel distance or displacement of the rear body portion toward the front body portion in response to a predetermined input force applied to the input push rod can be readily adjusted.
The sensor is supported by the coupling member and preferably comprises a permanent button magnet and a linear hall effect transducer. Preferably, the magnet and transducer are mounted in confronting relationship on an axis that is generally coextensive with the common axis so that the magnet and transducer are moveable relative to each other generally along the common axis. Electrical leads couple the transducer to one or more vehicle control systems, such as the brake light control system, an anti-lock braking control system (ABS) and a vehicle stability control system.
In accordance with the principles of the present invention, the transducer is operable to generate an electrical output that varies in magnitude with the amount of force applied to the input push rod through the brake pedal. As the input forces on the input push rod increase through driver input on the brake pedal, the gap distance between the permanent magnet and the linear hall effect transducer decreases, thereby resulting in a change in the output voltage of the transducer. The brake light control system is preferably configured to receive the output voltage signal generated by the transducer, and to use the magnitude of the output signal to determine whether the brake lights should be illuminated. The magnitude of the output voltage signal at which the brake lights are illuminated may be chosen to correspond to an input force on the input push rod that is indicative of an intended braking action by the driver.